var events = require("events");
// 创建eventEmitter 对象 

var eventEmitter = new events.EventEmitter();

// 创建事件处理程序 

var connectHandler = function connected(){
    console.log("① 连接成功");
    
// 触发 data_received 事件 
eventEmitter.emit('data_received');

}

//  绑定 connection 事件处理程序
eventEmitter.on("connection",connectHandler);

// 使用匿名函数绑定 data_received事件
eventEmitter.on("data_received",function(){
  console.log("② 数据接收成功")
})

// 触发connection 事件
eventEmitter.emit('connection');

console.log("③ 程序执行完毕")